Cross-linguistic comparisons permit us to disentangle the confound between universal mechanisms and language-specific content in current research on aphasia, while we address one of the most important issues in cognitive neurobiology, the issue of behavioral and neural plasticity. We propose new cross-linguistic studies of Broca's aphasia, Wernicke's aphasia and several control populations, using a set of languages and experimental procedures that are directly motivated by six basic findings from our research to date. Crosslinguistic variation: We have demonstrated that the "same" aphasic syndromes look very different from one language to another. In Years 8 - 12 we will concentrate on four languages (English, Italian, Hungarian and Chinese) that maximize the linguistic contrasts that have proven most important in this research. Performance deficits: These cross-linguistic differences suggest that language-specific knowledge (i.e. competence) is largely preserved in Broca's and Wernicke's aphasia, requiring an account of language breakdown based on deficits in the processes by which this preserved knowledge base is accessed and deployed (i.e. performance). This leads us to an expanded use of "on-line" or "real time" experimental procedures that yield information about how patients arrive at a correct or incorrect response in receptive and expressive language use. Selective vulnerability of morphology: Interacting with language differences, we find evidence for a selective impairment of grammatical inflections and function words. The proposed experiments are designed to distinguish between those aspects of morphology that are "at risk" and those that are "protected", within and across language types. Patient group similarities: Because we have found evidence for expressive and/or receptive impairments of grammatical morphology in several populations (including some non-neurological patient controls), we will conduct experiments that control for the contribution of a global reduction in perceptual and/or cognitive resources, in order to isolate those forms of grammatical impairment that are specific to particular types of aphasia from those that can be induced in normals under stressed conditions. Similarity of lexical & grammatical symptoms: Although morphology appears to be a quantitatively vulnerable domain, the grammatical symptoms displayed by these patients are qualitatively similar to their lexical symptoms. This leads to a detailed comparison of lexical and grammatical processing, in languages that rely to different degrees on word order, inflections and/or lexical contrasts to accomplish the same communicative goals. Patient group differences: We will investigate a set of proposed "neurolinguistic universals", contrasts between patient groups that hold up across very different language types. These studies will help to move the field of aphasiology toward a new model of intra-hemispheric organization, a model that can handle universal and language-specific differences between syndromes. In addition, these studies have practical implications for international communication about aphasia, for the development of aphasia batteries tailored to the specific characteristics of different languages, and for clinical services to the growing bilingual communities in our nation.